Optimization of solid phase microextraction coatings for liquid chromatography mass spectrometry determination of neurotransmitters

A simple solid phase microextraction method coupled to liquid chromatography mass spectrometry is introduced for the analysis of neurotransmitter compounds with a wide range of polarities in biological matrices. A novel “reversed” reverse-phase chromatographic method was developed without pre-column derivatization for the analysis of dopamine, serotonin, gamma aminobutyric acid and glutamate. New solid phase microextraction “in house” coatings using mixed-mode solid phase extraction particles were prepared, and used for the extraction of polar neurotransmitters. The polymer-support base reverse phase mixed-mode sorbents with strong ion exchange properties generally had higher extraction efficiencies compared to similar sorbents with weak ion exchange properties. The linear range was determined to be between 0.01 and 150 ng/mL for all the analytes, except for GABA, which was from 0.1 to 100 ng/mL. The limit of detection range was from 6 to 10 pg/mL for all the neurotransmitters, and the limits of quantitation were in the range of 20–35 pg/mL. The results demonstrate the potential of the SPME-LC–MS/MS technique for bioanalysis of small polar endogenous compounds, such as neurotransmitters, from various biological matrices using the mixed-mode sorbents as the extraction phase.